Bright light is a clinical intervention that can help people with chronic eye diseases such as macular degeneration recover lost visual function. For example, a study showed that among the 89% with macular degeneration, the average gain in reading acuity was greater than 0.2 log MAR (corresponding to the ability to read about 60% smaller letter size) when illuminance was increased from 125 lumens per square meter (lux) to 2050 lux. 125 lux is a lighting level that can be found in a typical home. However, many patients may achieve full acuity at 1500-2000 lux, and some may need over 5000 lux to achieve acuity.
Clinicians can test for response to increased lighting, but these tests are generally not controlled. For example, a patient's reading acuity may be evaluated using standard charts such as the MN read or SK read using ambient examining room light. The patient can then tested while wearing 4% transmission sunglasses. The assumption is generally that if reading acuity drops with the sunglasses (reduced light), then reading acuity would increase with bright light. However, this assumption may be inaccurate, for example, because increased light often introduces glare. Also, perceived brightness is generally non-linear, so the actual benefit from increased light may be smaller than assumed on the basis of the loss from reduced light.
In other cases, the doctor may employ a desk lamp to test for the benefit of brighter illuminance. However, such sources are rarely calibrated, and the illuminance is a sensitive function of their position with respect to the reading material or vision chart, so such testing is generally not repeatable. Also, a non-linear response of the eye may erroneously indicate less benefit at intermediate levels of illuminance than would actually be realized if testing were performed with a very bright light source. A test in the office with bright light can also be confounded by glare, from reflections off the eye chart or from sources such as a poorly positioned lamp. In such an examination environment, it can be difficult to control factors to obtain reproducible results, including glare, intensity and light uniformity at the plane of the chart.
An additional problem is that there is no standard method for converting the result of a lighting assessment into a recommendation for a lamp or light bulb that can produce the optimum lighting condition found in the exam, so the patient can duplicate the lighting at home, work or school. Without an existing technique to offer this recommendation, the assessment itself is of limited practical value to the patient.
Color and color temperature can also play a role in eye strain and comfort in reading, and are factors that can be considered in selecting lighting. Color, or tints of glasses can also play an important role in outdoor vision performance. Accordingly, a problem exists because no standard test device or technique exists to determine a patient response to increased illuminance including providing reproducible test conditions and control of factors that can influence results, allows for testing with different colors of light, and has a quantified output that can be entered into a medical record, and no technique or system for the clinician to offer a recommendation on how the patient can duplicate ideal lighting conditions after leaving the office.